Although liquid crystals have been known for over 100 years, the interest in liquid crystals has increased dramatically in the last 20 years, particularly for use in electro-optical switching and display devices.
For many types of liquid crystal displays, especially the supertwisted nematic-liquid crystal display (STN-LCD), the superbirefringence (SBE), or the double-supertwist (D-STN), it is necessary that a thin alignment layer be deposited on a glass substrate to orient liquid crystal molecules at a predetermined pretilt angle on the glass surface. It is further advantageous or necessary that this alignment layer be capable of establishing a pretilt angle of 5.degree. or more, so that liquid crystal twist angles in the range of 240.degree. to 270.degree. can be achieved.
Both inorganic and organic alignment layers for liquid crystals are known in the art. An example of an inorganic material is SiO, which is deposited by evaporation onto the glass substrate. Although SiO deposition has the advantage of providing pretilt angles of greater than 10.degree., this material is not considered to be commercially feasible.
Organic polymers, most notably nylon and polyimides, have also been used as alignment layers. The organic polymer is first deposited on the glass substrate by any suitable means, such as spin coating, screen printing, or roller coating. The polymer is then cured, then rubbed with fabric in a chosen direction to create a surface which provides alignment for the liquid crystal as well a pretilt angle. This angle should be as high as possible for fast response STN-LCDs. Recently, Dubal et al., in U.S. Pat. No. 5,331,081, incorporated herein by reference has disclosed the use of perfluorinated polyamides as alignment layers for liquid crystal switching and display devices. These perfluorinated polyamides reportedly have the advantage of providing suitable orientation layers which can be cured at temperatures below 250.degree. C., and which provide a surface tilt angle of 9.degree..
There is a continuing interest in developing new alignment layer materials which provide high surface tilt angles and can be cured at temperatures below 50.degree. C.